This invention relates to drilling wells, and more particularly, to methods and apparatus for drilling wells much more efficiently and effectively so as to substantially reduce the multi-million dollar cost of drilling a well.
It is well known in the drilling industry, and particularly in the field of drilling for oil, natural gas and other hydrocarbons, that drill strings comprise a large plurality of tubular sections, hereinafter xe2x80x9ctubularsxe2x80x9d, which are connected by male threads on the pins and female threads in the boxes. It is also well known that such tubulars must be added to the drill string, one-by-one, or in xe2x80x9cstandsxe2x80x9d of 2 or 3 connected tubulars, as the string carrying the drill bit drills into the ground; a mile more below ground being common in the oil drilling art. For various reasons during the drilling, and after the bore hole has been drilled, it is necessary to withdraw the drill string, in whole or in part. Again, each tubular or stand must be unscrewed, one-by-one, as the drill string is brought up to the extent required.
With prior art systems, each time that a tubular is added or removed it is necessary to stop the drilling process, and the circulation of drilling fluid. This presents a costly delay in the overall drilling operation. This is because the circulation of drilling fluids is extremely critical to maintaining a steady down hole pressure and a steady and near constant Equivalent Circulating Density (ECD) as is well known in the drilling art. Also, when tripping the drill string into or out of the well, the lack of continuous circulation of a drilling fluid causes pressure changes in the well which increases the probability of xe2x80x9ckicksxe2x80x9d as is well known.
In addition to the drilling operation, the placement of casings in the bore hole is also necessary. As in the case of tubulars, the placement of casing sections in the prior art presents the same fundamental problems. That is, the flow of drilling fluids must be halted, and the drill string must be withdrawn in its entirety before the casing can be run into the well, which in some instances requires circulation of fluids and rotation of the casing.
The present invention substantially reduces the time and cost of drilling operations by making it possible to continuously circulate drilling fluids while tubulars are added or removed, and also as casing strings are run into the bore hole. In addition, the present invention makes it possible to continue to rotate the drill string, if desired, while adding or removing tubulars. Bearing in mind that hundreds of tubulars are required per mile of drill string, the present invention eliminates hundreds of interruptions of the circulation of drilling fluids, and a like number of breaks in the rotation of the drill string and the drilling operation per mile of drilling.